well, since we are about to intercept @ARGV, we can expect string of '--help', may be '-help' or even short versions such as '-h' or '--h' (though the latter seems odd).
with version 5.10 or newer, smart match comes handy. i'd take 'help' out from GetOptions(), and prior to calling it, intercept @ARGV and call help() if match found. i like to separate the whole message printing in its own sub for easy modification on the text.

now, the presence of either -h --h -help --help will trigger help message.

$ ./ghosh.pl --help
This is help message
$ ./ghosh.pl --abc --help
This is help message
$ ./ghosh.pl --abc -help
This is help message
$ ./ghosh.pl --abc -h
This is help message
$ ./ghosh.pl --abc --h
This is help message
$ ./ghosh.pl --abc abc -h
This is help message
$ ./ghosh.pl --abc abc
You have choosen "abc" as abc
$ ./ghosh.pl --h
This is help message
$ ./ghosh.pl -h --abc
This is help message